Pretension is definitely a risk factor for stroke and both types of stroke have a high blood pressure as a risk factor. 85% of strokes are from blood vessel blockages and high blood pressure can lead to stiffened arteries and other conditions that contribute to these blockages. The remainder of strokes are from ruptured blood vessels either because they were weakened by a lifetime of high blood pressure or because the pressure was too great in an already weakened artery. In both cases, stroke is a risk from untreated blood pressure. It's also possible that lowering our blood pressure too fast can cause a stroke. This is why your ER or primary doctor doesn't immediately lower your pressure to 120 over 80.